This invention relates to compositions containing acetyl esterases for enhancing digestion of fiber in animals, including mammals and birds, and to methods for improving nutrient digestion by supplementation, feeds, feed concentrates and mineral supplements with compositions comprising acetyl esterase, especially a composition derived from culturing a ruminal isolate of Orpinomyces, said isolate named Strain KY herein.
Supplementation of animal feed with exogenous enzymes for purposes of improvement of animal performance is known in the art. Such use is related to the central role of digestive enzymes, either secreted by the animal or by microbes harbored in the animal""s gut, in digestion of foodstuffs. For the most part, the major success in use of dietary supplementation of exogenous enzymes in monogastric species has been achieved in the area of overcoming negative effects of antinutritional factors. In animals whose diet comprises primarily forages and other plant materials, the use of exogenous enzymes has focused on improvements in fiber digestion.
Plant materials contain significant proportions of insoluble, structural polysaccharides. Even such as ruminants and equine species adapted to subsist on a diet of plant materials, digestion of forages is often not complete. Overall feed digestibility and nutrient availability to the animal is not maximal, and the full benefit of consumption of forage is not realized, as reflected in animal performance. Accordingly, attempts at supplementation of animals with exogenous enzymes have been made. For example, U.S. Pat. No. 5,720,971 to Beauchemin et al. discloses a fibrolytic enzyme supplement, primarily containing cellulase and xylanase, which is sprayed on forages and allowed to incubate for a period of hours prior to ingestion. The result is a feed composition consisting of forages with improved digestibility for ruminant species. U.S. Pat. No. 5,948,454 to Virkki et al. teaches a modified cellulase-containing composition suitable for treating crops to improve storage characteristics and feed values.
The enzyme supplements cited above are generally effective for their intended purposes. However, further improvements are possible. For example, each of the enzyme supplements cited above are used as pretreatments of forages prior to feeding those forages to animals. This adds an additional step to the process, and may result in a feed which, though more digestible, has a limited shelf life and may require specialized storage conditions related to temperature or moisture sensitivity. Additionally, the potential for use of alternative enzymes for improvements in fiber digestibility, particularly in species whose diet comprises primarily forages or other fibrous feeds, has to date received limited study.
Esterases produced by various anaerobic bacteria and fungi are responsible for removing side groups normally present in plant cell wall polysaccharides. Other esterases such as feruloyl and coumaroyl esterases also break down chemical bonds central to hemicellulose-lignin associations. While not wishing to be bound to any particular theory, it is believed that the actions of esterases increase enzyme accessibility to the backbones of plant cell wall polysaccharides and influence overall plant cell wall structure, thereby improving digestibility. There remains a need in the art for improvements in the economics of agriculture, especially as related to animal feeds. This can be accomplished, at least in part, using alternative enzyme supplements for enhancing fiber digestibility in, e.g., ruminant, equine, porcine, and avian species. There is further a need in the art for alternative enzyme supplements capable of enhancing the efficacy of prior art enzyme supplements for enhancing fiber digestibility in, e.g. ruminant, equine, porcine, and avian species. Ruminant animals of particular economic importance include cattle, sheep, buffaloes and goats. Others include camels, guanaco, llamas, wapiti, antelope, musk oxen, giraffes and others. Improving the efficiency of feed utilization improves the economics of agriculture, thus providing a benefit to the agricultural industry and to society. In addition, captive wild ruminants and other fiber-eating animals can benefit from the present invention.
The present invention provides compositions comprising acetyl esterase; these compositions are useful for enhancing fiber digestion. The compositions can be used as dietary supplements for animals, especially for those animals with a fiber-rich diet. The animals which benefit from such supplements include, without limitation, ruminant, equine, porcine, caprine, ovine, and avian species, e.g., poultry. The acetyl esterase containing compositions can be dry formulations or wet formulations with crude fermentation materials or purified enzyme. In a specifically exemplified embodiment, the enzyme composition desirably is administered in an amount sufficient to provide from about 1 to about 10 U/kg of digesta in the rumen. The composition can be mixed with feed, silage, hay or grain, or it can be incorporated into mineral supplements to be fed to the animals or into a concentrated feed component for ease of mixing into the bulk feed preparation.
The acetyl esterase of the present invention may be isolated from an anaerobic microorganism, such a ruminal fungus or a ruminal bacterium. In a preferred embodiment, the acetyl esterase of the present invention may be isolated from or produced in cultures of anaerobic fungi including, but not limited to, Piromyces, Neocallimastix, Caecomyces, Anaeromyces and Orpinomyces, or combinations thereof. Alternatively, the acetyl esterase for use in the present invention may be isolated from cultures of or produced in anaerobic bacteria such as Butyrivibrio, Clostridium, Fibrobacter, Prevotella, Ruminobacter, Ruminococcus, Selenomonas or Streptococcus. Other potential bacterial sources of acetyl esterase include, but are not limited to, Bacillus, Pseudomonas, Streptomyces, Thermonospora, Caldocellum, Thermoanaerobacter, or combinations thereof. As specifically exemplified, the acetyl esterase is produced by a ruminal isolate of Orpinomyces, strain KY. The strain described herein does not produce detectable cellulase or xylanase activity in the extracellular milieu, although the majority of the acetyl esterase activity is extracellular.
Another aspect of the invention is a method for enhancing fiber digestion in an animal, mammalian or avian, by feeding an effective amount of an acetyl esterase-containing composition to said mammalian or avian species. The acetyl esterase containing composition of the present invention may be fed to any animal for which forages or fibrous foods comprise a significant percentage of the diet, with the proviso that there is sufficient acetyl esterase to improve the digestion of the plant fiber material in the diet of the animal. It is envisioned that for a ruminant, for example, a dairy cow, the acetyl esterase is fed in an amount sufficient to result in a specific activity in the rumen of about 1 to about 10 U/kg of digesta (rumen contents). Desirably, a mature bovine is fed from about 50 to about 5000 units of acetyl esterase per day, depending for example on diet and on whether a female bovine is lactating or not. The amount of enzyme activity to be consumed by the animal is determined by rumen (or other relevant digestive organ) capacity.
In yet another embodiment of the present invention, a method for enhancing fiber digestion in a mammal is provided comprising feeding an effective amount of an acetyl esterase-containing composition in conjunction with known, prior art enzyme supplements to said mammal to enhance fiber digestibility. The acetyl esterase-containing compositions of the present invention are especially useful in supplements to the diets of animals including, but not limited to, cattle, horses, sheep, goats, swine and poultry.
Also embodied within the present invention is the anaerobic fungus isolated from the rumen, which fungus is the specifically exemplified source of acetyl esterase. This fungus is a polycentric fungus, and without wishing to be bound by theory, it is believed to be a member of the genus Orpinomyces.